LMH7322_14 Datasheet, PDF (16/33 Pages) Texas Instruments – Dual 700 ps High Speed Comparator with RSPECL Outputs

LMH7322
SNOSAU8H – MARCH 2007 – REVISED MAY 2011
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The DAP and the VEE Pins
To ensure that both VEE pins are operating at the same voltage, both pins are connected to the DAP, and thus
to each other, through bond wires. As a consequence, the DAP is at the same potential as the VEE pins and can
be used to connect the device to the minimum supply voltage. A more solid VEE connection is obtained if the
two VEE pins and the DAP are all connected to the minimum supply on the PCB, rather than an indirect
connection through the internal bond wires.
To protect the device during handling and production two anti-parallel connected diodes are connected between
both VEE pins. Under normal operating conditions these diodes are shorted via the DAP.
The DAP (Die Attach Paddle) functions as a heat sink which means that heat can be transferred using vias
below this pad to the copper plane VEE is connected to.
Figure 21. DAP Connection
Interface Between Logic Families
As can be seen in the typical schematics (see Figure 1) the LMH7322 can be used to interface between different
logic families. The feature that facilitates this property is the fact that the input stage and the output stage use
different positive power supply pins which can be used at different supply voltages. The negative supply pins are
connected together for both parts. Using the power pins at different supply voltages makes it possible to create
several translations for logic families. It is possible to translate from logic at negative voltage levels such as ECL
to logic at positive levels such as RSPECL and LVDS and vice versa. The drawings in the next paragraphs do
not show the output resistors except the first one. This is intentionally done for simplicity. All outputs need an
output resistor to a termination voltage or to the negative rail as can be seen on the front page in the Typical
Application of an ECL to RSPECL converter.
Interface from ECL to RSPECL
The supply pin V_CCI can be connected to ground because the input levels are negative and the V_CCO pin must
operate at 5V to create the RSPECL levels (see Figure 22). When working with ECL, the negative supply pin
(V_EE) can be connected to the −5.2V ECL supply voltage.
5V
+
ECL driver
Coupled
transmission line
Line Termination
IN+
IN- _1/2
LMH 7322
RHYS
Q
RS-PECL
OUTPUT
VOH = 3.9V
VOL = 3.5V
Q
RT RT
VT = VCCO-2V
or
VT = VEE
VT
10k
LE levels referred to VCCO
-5.2V
+
Figure 22. ECL TO RSPECL
16
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